1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system, and more specifically relates to a sheet processing apparatus having an alignment function for aligning a sheet-shaped member such as paper, a recording sheet, transfer paper, or an OHP sheet that is carried in (simply referred to as a “sheet” in the specification including claims), and an image forming system including the sheet processing apparatus, and an image forming apparatus such as a copier, a printer, a facsimile, and a digital MFP.
2. Description of the Related Art
Conventionally known is an apparatus called a finisher including a stapler that stacks sheets discharged from an image forming apparatus into a staple tray, aligns them in a sheet conveying direction (what is called a vertical direction, and the same shall apply hereinafter) and a direction orthogonal to the sheet conveying direction (what is called a width direction, and the same shall apply hereinafter), and then binds the sheets.
An invention described, for example, in Japanese Laid-open Patent Publication No. 11-130338 is known as this type of apparatus. This publication discloses a sheet processing apparatus including a staple tray that accepts and stacks sheets discharged from an image forming apparatus, a trailing end fence against which ends in a conveying direction of the sheets stacked on the staple tray abuts to align the sheets, and a stapling unit that performs a stapling process on the end of the bundle of sheets aligned by the trailing end fence. The sheet processing apparatus includes a pressing member that can move in a thickness direction of the bundle of sheets stacked on the staple tray, and presses a top surface of the sheets in the vicinity of the trailing end fence whenever the predetermined number of sheets is discharged onto the staple tray. The pressing member is for pressing a bundle of sheets to prevent the trailing ends of the sheets from bending and buckling.
In a case of end surface binding performed by the stapler, when sheets are stacked on the staple tray, if the end of a sheet on which the stapling process is performed is curling up or bulging in the thickness direction due to the influence of a curl and the like of the paper, the sheets may not be aligned in vertical and horizontal directions, and thus paper alignment accuracy may be reduced. Hence, in Japanese Laid-open Patent Publication No. 11-130338, a bundle of sheets is pressed by the pressing member in a state where the trailing end of the bundle of sheets is in contact with the reference fence. This pressing member corresponds to a pressing member (trailing end press lever) 110 in FIG. 1 to be described later. The pressing member 110 is located at a lower end of a trailing end reference fence 51 so as to be possible to press the trailing end of a sheet bundle SB housed in the trailing end reference fence 51, and can reciprocate in a substantially vertical direction to an end surface binding processing tray F (refer to FIG. 7 to be described later).
However, in a known sheet holding configuration, the pressing member for pressing and holding a sheet bundle is configured to press a position away from the stapler, considering interference with the stapler. Therefore, a bend and the like occur on the sheet bundle when the bundle is bound with a staple, and it is difficult to obtain excellent alignment accuracy.
Therefore, there is a need for a sheet processing apparatus and an image forming system capable of reliably aligning a bundle of sheets in a sheet conveying direction and a direction orthogonal to the sheet conveying direction even if a curl, a bulge and the like occur on the bundle of sheets to thereby ensure excellent alignment accuracy.